SINGAPORE (AP) —
President Donald Trump and North Korea's Kim Jong Un kicked off a momentous summit Tuesday, with Trump declaring the two would have a "great discussion" and Kim saying they had overcome "obstacles" to get to this point.

Before a row of alternating U.S. and North Korean flags, the leaders shook hands at a Singapore island resort, creating an indelible image of two unorthodox leaders as they opened a conversation that could determine historic peace or raise the spectre of a growing nuclear threat.

Trump and Kim planned to meet one on one for most of an hour — joined only by interpreters.

Then aides to each were to join for more discussions and a working lunch.

But even before they met, Trump announced plans to leave early, raising questions about whether his aspirations for an ambitious outcome had been scaled back.

The first meeting of a sitting U.S. president and a North Korean leader was the product of dizzying weeks of negotiations over logistics and policy.

Up early in Singapore, Trump tweeted with cautious optimism: "Meetings between staffs and representatives are going well and quickly... but in the end, that doesn't matter. We will all know soon whether or not a real deal, unlike those of the past, can happen!"

In the run-up to the talks, Trump had hopefully predicted the two men might strike a nuclear deal or forge a formal end to the Korean War in the course of a single meeting or over several days.

But on the eve of the summit, the White House unexpectedly announced Trump would depart Singapore by Tuesday evening, meaning his time with Kim would be fairly brief.

And Secretary of State Mike Pompeo sought to keep expectations for the summit in check.

"We are hopeful this summit will have set the conditions for future successful talks," Pompeo said, describing a far more modest goal than Trump had outlined days earlier.

The sudden change in schedule added to a dizzying few days of foreign policy activity for Trump, who shocked U.S. allies over the weekend when he used a meeting of the Group of Seven industrialised economies in Canada to alienate America's closest friends in the West.

Lashing out over trade practises, Trump lobbed insults at his G-7 host, Canadian Prime Minister Justin Trudeau. Trump left the summit early, and as he flew to Singapore, he tweeted that he was yanking the U.S. out of the group's traditional closing statement.

As for Singapore, the White House said Trump was leaving early because negotiations had moved "more quickly than expected," but gave no details about any possible progress in preliminary talks.

On the day before the meeting, weeks of preparation appeared to pick up in pace, with U.S. and North Korean officials meeting throughout Monday at a Singapore hotel.

The president planned to stop in Guam and Hawaii on his way back to Washington.